/Engine/Plugins/FX/Niagara/Source/NiagaraEditor/Public/NiagaraGraph.h
This is the type of action that occurred on a given Niagara graph. Note that this should follow from EEdGraphActionType, leaving some slop for growth.
enum ENiagaraGraphActionType { GRAPHACTION_GenericNeedsRecompile = 0x1 << 16, }